ONGC Videsh's cash offer is 1,250 pence per share, compared with a share price on August 22 of 1,240 pence, and is a 61.9% premium on the share price on July 11 – the day prior to Imperial's confirmation of talks with a suitor.

The London listed oil producer has operations in Russia’s Tomsk region and plans to be producing more than 25,000 bpd by the end of this year. It has Russian registered reserves of 450 million barrels.